1. Technical Field
The present invention relates to a bearing wear detecting device for detecting wear of bearings of a motor.
2. Description of the Related Art
The principal usage of a conventional canned motor is for driving a pump. For example, in case of a canned motor pump, it is not possible to visually observe the interior of the motor, because the canned motor and the pump are formed in an integral body to prevent fluid leakage. An impeller of the pump is rotated by a rotor of the canned pump, which is in many cases supported by bearings that are adapted to be lubricated with pump fluid. In order to operate the canned motor efficiently, it is essential to observe the state of the bearings, i.e. degree of wear, from outside.
There have conventionally been provided various bearing wear detecting devices that call for disposing an axial position detecting coil at each axial end of a stator of a canned motor and comparing the voltages respectively induced in the two axial position detecting coils in order to detect the axial position of a rotor and thereby estimate the amount of axial wear of bearings based on the axial position of the rotor, which is supported by the bearings. The aforementioned voltages are induced in the axial position detecting coils, which are respectively provided at the two axial ends of the stator, by rotation of the rotor when the motor is operated.
An example of bearing wear detecting devices of this type is disclosed in Japanese Patent Laid-open No. 2002-153018, which offers two ways of providing an axial position detecting coil at each axial end of a stator: one of them calls for providing a small core portion by forming notched grooves near the end of a tooth of the stator and winding an axial position detecting coil around the core portion, and the other way calls for providing a space in the surface of each axial end of the stator and disposing therein a core around which an axial position detecting coil is wound.
With such a bearing wear detecting device, in order to precisely detect the axial position of the rotor based on difference between the voltages respectively induced in the axial position detecting coils at the two ends of the rotor, zero adjustment is essential. The aforementioned zero adjustment calls for matching the axial position of the rotor, which is supported by bearings, with the signal representing the difference between the voltages respectively induced in the axial position detecting coils at the two axial ends of the rotor. This matching is done by moving the rotor in either axial direction in the state where rotation of the rotor resulting from operation of the canned motor is inducing voltages on the detection coils. The rotor is moved by an adjusting device or any other appropriate means to move the rotor in an axial direction or a radial direction while the canned motor is operated.
As disclosed in Japanese Laid-open Patent Publication No. 08-43010 and published Japanese translation of PCT International publication No. 2001-505310, there is provided a position detecting device that calls for providing the rotor or the rotor shaft of a canned motor with a position detection target made of a magnetic material, and disposing a plurality of detection coils around a stator can, wherein the detection coils are wound around such a member as a magnetic piece or a core and circumferentially arranged at regular intervals so as to face the cylindrical outer surface of the position detection target. The bearing wear detecting device is adapted to apply high frequency signals to the detection coils during operation of the canned motor, detect the inductances of the detection coils to which the frequency signals have been applied, and determine the axial position as well as the radial position of the rotor based on changes in the inductances of the detection coils.
The conventional bearing wear detecting device described above calls for providing a small core portion by forming notched grooves near the end of a tooth of the stator and winding an axial position detecting coil around the core portion, or providing a space in the surface of each axial end of the stator and disposing therein a core around which an axial position detecting coil is wound. In either case, installation of the axial position detecting coils causes inconvenience and requires a number of man-hours as it necessitates processing of the stator.
Furthermore, voltage induced in each axial position detecting coil is affected by not only the axial position of the rotor but also the radial position of the rotor. Therefore, changes in radial position of the rotor must be taken into consideration to detect the axial position of the rotor or perform axial zero adjustment.
The aforementioned position detecting device is provided with a plurality of detection coils around the stator can. As these detection coils have to be wound around a magnetic piece, a core, or the like, installation of the axial position detecting coils causes inconvenience and requires a number of man-hours. Furthermore, as output from each detection coil is affected also by the radial position of the rotor, changes in radial position of the rotor must be taken into consideration to detect the axial position of the rotor or perform axial zero adjustment.